This invention relates to fan constructions for use with, for example, internal combustion engines employing circulating liquid coolants and radiators.
Prior art of possible relevance includes the following U.S. Pat. Nos. 2,668,523 issued Feb. 9, 1954 to Lamb; 3,680,977 issued Aug. 1, 1972 to Rabouyt et al; and 3,794,001 issued Feb. 26, 1974 to Birch et al.
In most applications utilizing internal combustion engines having circulating coolant and radiators, the radiator is mounted rigidly on a frame while the engine is resiliently mounted on the frame. A fan driven by the engine is generally mounted on the engine itself and rotates within an orifice in a shroud fixedly attached to the radiator. The engine will move in relation to the radiator due to deflection in the respective mounting components. Where the apparatus is part of a vehicle, the relative movement is accentuated by deflection of the frame caused by unevenness in the terrain over which the vehicle may be traveling. Considerable clearance must be provided between the tips of the fan blade and the orifice in the radiator shroud to allow such movement to occur without the tips of the fan blades engaging the periphery of the orifice.
In trucks, for example, it is common practice to provide clearances of one to two inches between the fan tips and the shroud to accommodate the large relative movement. Such large clearances result in air recirculation and loss of efficiency in the fan construction. As a consequence, in order to adequately cool such engines, it is necessary to employ radiators and fans considerably larger than those theoretically necessary.
Because of the general trend to the use of higher horsepower engines, particularly in vehicles, and the resulting greater cooling requirement, the practical limits for frontal area of radiators have, for all intents and purposes, been reached. In conventional trucks, an increase in radiator size would reduce the operator's visibility, while with cab over engine trucks, increasing the size of the radiators would require a reduction in the leg room for the operator. The situation is further complicated by the trend towards the use of air conditioning and automatic transmissions on such trucks with the corresponding additional heat load to the cooling system.
Moreover, concern for emissions of engines and increasingly stringent regulations appear to require a greater heat rejection per horse power from the engine to achieve emission standards, again increasing the heat load. Regulations regulating noise level are of consequence as well. Fans are large contributors to the overall noise generated by vehicles, the noise generated being proportional to fan speed.
Thus, there is a real need for a fan construction wherein fan speed may be reduced to lower noise levels while the air flow generated by the fan is increased to accommodate increasing cooling requirements in such systems.